Some devices like the arduino have an on-board usb to serial chip (remove the AVR chip to use it)

A second usb development board can also be programmed as a usb to serial converter.

AVR USB development board

Make sure it is working at 5V and that is has a chip among the following: at90usb82, at90usb162, at90usb646, at90usb647, at90usb1286, at90usb1287, atmega16u2, atmega32u2, atmega16u4, atmega32u4
Examples:

Click on the COM port that matches the "Silicon Labs CP210x ... (COMX)" COM port in the device manager (or whatever the name of your USB to UART board is). This is a trick to make the Arduino Builder tool look for a new COM port.

The following message should appear: "Forcing reset using 1200bps open/close on COMX...".

Serial port settings

On Windows the driver for FTDI chips (e.g. FT232R, FT230X, FT231X...) provides a "Latency Timer" setting than should be set to 1ms for optimal performance.
The procedure is detailed on the FTDI website: link.

Next Tutorial

Now that your adapter is ready you can follow the instructions on the Quick Start page.